The present invention relates generally to tilt control mechanisms for chairs, and in particular, to synchrotilt control mechanisms.
In general, tilt control mechanisms are mechanical devices that control the tilting of a chair when occupied by a user. To provide improved aesthetics, and to avoid interference with use of the chair, tilt control mechanisms are typically mounted underneath the chair. Tilt control mechanisms also typically employ a spring, or other energy storing device, to control the rate at which the chair tilts and to return the chair to an upright position when the user is not leaning back in it. Tilt control mechanisms generally include an adjustment device that permits the user to vary the upward force exerted by the spring, thereby allowing the chair to tilt downwardly and rearwardly more or less easily depending on the upward force exerted.
Tilt chairs come in a variety of forms, although most include a seat and a back. For example, some tilt chairs have a seat maintained in a fixed position, allowing only the back to tilt rearwardly and downwardly. In another form, tilt chairs have the seat and back rigidly connected whereby they tilt rearwardly and downwardly at the same rate. Both of these types of chairs have disadvantages. For example, a fixed seat and back arrangement does not allow the user's body cavity to open up as the user tilts rearwardly. An open body cavity allows for better circulation and spinal curvature, thereby improving the user's comfort and physical health. Moreover, many of the previous designs pivot about a point near the base or support of the chair where the user's center of gravity is located. As a result, when the chair is tilted rearwardly, the user's feet are lifted off of the floor by the front part of the seat, thereby generating pressure on the underside of the user's thighs, making the user uncomfortable and inhibiting the user's circulation. Synchrotilt control mechanisms were designed to overcome some of these problems.
With synchrotilt mechanisms, the back and seat tilt simultaneously, but at different rates. Generally, the back tilts at a faster rate than the seat so that the body cavity opens. An example of a prior synchronous tilt control mechanism may be found in U.S. Pat. No. 4,390,206, entitled Synchrotilt Chair Control and issued to Faiks, et. al.
Typically, synchrotilt chairs have the seat and back interconnected so as to actuate the synchronized tilting of the back with the seat. For example, the seat and back may be directly pivotally connected as set forth in the Faiks, et. al. Patent. Other synchrotilt control mechanisms employ linkage mechanisms to interconnect the seat and back and to actuate the synchronous tilting. In either type, the synchrotilt control mechanism comprises complex interconnecting moving parts. The majority of these prior art tilt control mechanisms permit only backward tilting of the chair, separately or together at differing rates. To counter that problem, U.S. Pat. No. 5,029,940, entitled Chair Tilt and Chair Height Control Apparatus and issued to Golynsky, discloses a tilt mechanism permitting both forward and backward tilting of the chair seat and back using the same mechanism. That mechanism uses a four-bar linkage mechanism, whereby the seat is interconnected with the back. When the seat is tilted upwardly, the back of the chair is also caused to be tilted upwardly. Accordingly, the back can protrude into the user's back thus making use in the forward tilt position uncomfortable.